Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 262352
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
752 PM EDT WED OCT 26 2016
Portions of the forecast area got an early taste of winter today.
To recap, the northern Detroit suburbs and points north saw a mix
of snow and rain through a good portion of the afternoon. The tri
cities and the central thumb had almost entirely all snow. The
snow was actually falling at a moderate pace at times. The warm
ground temps inhibited accumulations on roads. However, there
have been reports of one to almost two inches on elevated surfaces
extending along a line from roughly Midland County to Lapeer
County. This does not break the earliest record of measurable snow
in Southeast Michigan which occurred on October 12, 2006.
A strong influx of deep layer moisture into Lower Mi has been
occuring in advance of a compact mid level wave now over Wisconsin.
This moisture has been intersecting a mid level frontal boundary
over Lower Mi. Meanwhile, easterly surface flow throughout the
afternoon (coming from srn Ontario where sfc dewpoints are in the
20s) sustained enough low level dry air to bring wet bulb zero
heights below 1k ft within the region of strongest ascent (from
Central Mi into the thumb). This forcing held nearly stationary
for much of the afternoon, leading to a localized region of
significant cooling and persistent snowfall.
The influx of deep moisture transport will persist through roughly
06Z before it slowly shifts east. There has already been some
disruption to the mid level fgen across the north. Although
recent hi res solutions suggest the fgen holding together and
possibly reintensifying during the night, strengthening low level
moisture advection will boost wet bulb zero heights during the
course of the night. There has been a subtle upward trend in sfc
dewpoints across the the forecast area which supports this. Recent
model soundings suggest this moistening will lift wet bulb zero
heights above 12k ft and thus transition lingering snow over to
all rain by midnight. The mid level dry slot already punching into
Lake Mi will then rotate across most of the area late tonight,
transition rain showers over to drizzle. Overall the current
forecast has a reasonable handle on this. Just some minor updates
to temps and timing of the change over to rain in the north will
Issued at 711 PM EDT Wed OCT 26 2016
Deep layer moisture transport associated with low pressure over
northern Illinois is interacting with an elevated front over Lower
Mi. Enough cooling occurred on the north side of this boundary at MBS
to cause precip type to be mainly snow all afternoon and evening.
Low level moistening and subtle warming will slowly change the snow
to all rain at MBS over the next 1 to 3 hours. The rest of the
terminals are now seeing mainly rain. The surface low will track
east along the MI/OH border toward daybreak Thurs. Continued
moisture advection into the region will result in more persistent
IFR (and perhaps some brief intervals of LIFR) during the course of
the evening and into the overnight. Mid level dry air will advance
across the southern portions of the area coincident with the surface
low passage. The result be a transition from numerous/widespread
showers to areas of drizzle.
For DTW...Through the evening hours metro will reside along the
southern edge of the higher low level moisture. The result will be
that the bulk of the lower clouds will be north of metro. The
approach of the surface low overnight will bring a better influx of
low level moisture into metro, with IFR and some LIFR ceilings in
light showers and/or drizzle expected just prior to daybreak. The
easterly winds will persist through a good portion of the overnight.
There will be some gusts which top 20 knots at times this evening
before mixing lowers a bit overnight. The gradient will relax late
tonight with the approach of the surface low. This will support
generally light and somewhat variable winds by daybreak Thurs, with
northwest winds develop late in the morning as the low heads east
of the region.
//DTW Threshold Probabilities...
* High in ceilings below 5000 feet.
Issued at 342 PM EDT Wed OCT 26 2016
An upper level shortwave trough is now tracking into the Northern
Great Lakes with the associated surface low over western Illinois as
of 19Z. The leading flank of precipitation has developed with good
moisture advection over the warm front with an active 850-700mb fgen
band and supporting region of isentropic ascent. Overall the lead
band of showers is behaving as expected, outside of a bit more sleet
at the onset as dewpoints in the upper 20s kept wet bulb temps well
below the 40 degree temps around the region. As the deeper moisture
moves in and dewpoints rise to the mid 30s, precip will change to
all rain for the duration of the event this evening and tonight for
most locations. The Thumb and Saginaw may hold onto the mix precip
longer as they are farther removed from the low itself which will
track along the MI/OH border. Soundings also support saturation in
the ice crystal layer for several more hours before temperatures
warm slightly and moisture no longer resides in the layer below -
10C. Early reports out of the Cadillac area are of some minor slushy
accumulation from the heavier bands. Cannot completely rule out some
minor slush on the ground around Midland through this evening, but
won`t last long before melting. Mixed precip should end later this
evening turning to all rain for the overnight period as higher
dewpoints work into the area closer to the center of the low. A dry
slot lifting into southwest lower looks like it has reached it`s
peak northward extent as showers regenerated filling it back in.
This will result in a brief lull for locations south of I94 this
afternoon but additional showers will slide through tonight.
The heaviest showers will work off to the east early Thursday
morning with some scattered showers lingering on through the
morning. Cold air advection with cyclonic flow behind the system
will drop 850mb temps from about 1C this afternoon to -4C on
Thursday which will result in strong low level lapse rates. Moisture
will locked below 800mb in this active region which will result in
some afternoon showers. Models are advertising some CAPE in the
afternoon which may result in some graupel forming in the stronger
showers. Will not see much of an improvement in temperatures
Thursday with highs only in the mid/upper 40s. Zonal flow in the mid
level will bring a flat ridge and warmer air into the area Friday
resulting in highs back in the mid 50s. The next wave will dive from
the Northern Plains through the Northern Great Lakes Friday night.
Looks dry on the south side of the system over lower MI but a cold
front sweeping across the area late Friday night into Saturday
morning will need a chance pop.
Low Pressure centered over upper Michigan on Friday afternoon will
continue to track to the east east through the weekend. Weak chances
for precipitation are possible during the day on Saturday,
especially over the northern thumb areas. High Pressure returns for
Sunday/Monday. At this time, models are showing a stronger weather
system that will begin moving into southeast Michigan on the late
Low pressure will track from northern Illinois to extreme Southern
Ontario by Thursday morning. Easterly winds will continue to
strengthen this evening and overnight as the low approaches. Speeds
will decrease after about 5 AM over Lake St Clair and Western Lake
Erie as the low passes overhead, while remaining strong and turning
more to the northeast over Lake Huron. Gusts this evening through
Thursday look to remain under gale force with peak winds around 30
knots. The strong and persistent onshore flow will also generate
large waves over the nearshore waters, which will continue into
Thursday for Lake Huron. High pressure will slowly build into the
Central Great Lakes late Thursday and Thursday night, allowing winds
and waves to decrease.
Numerous rain showers, at times mixed with sleet or snow, will
continue to spread into Southeast Michigan through the remainder of
the afternoon. Coverage and intensity will increase this evening and
overnight with widespread and steadier rainfall expected. Potential
for snow/sleet will also decrease this evening from south to north
as deeper moisture and higher dewpoints arrive. Rain will taper off
to showers tomorrow morning before ending tomorrow afternoon.
Rainfall totals are still expected to range between one-half and
three-quarters of an inch. Dry weather is expected Thursday night
and Friday, with just a small chance of light showers Friday night.
Lake Huron...Small Craft Advisory until 10 PM EDT Thursday FOR LHZ421-441>443.
Small Craft Advisory until 9 AM EDT Thursday FOR LHZ422.
Lake St Clair...Small Craft Advisory until 4 AM EDT Thursday FOR LCZ460.
Michigan waters of Lake Erie...Small Craft Advisory until 4 AM EDT Thursday FOR LEZ444.
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